Crystal oscillator ultramicrometer



p 16, 1952 G. RALSTON ET AL 2,611,020

CRYSTAL OSCILLATOR ULTRAMICROMETER Filed March 16, 1949 2 SHEETS -SHEET 1 I Curve B 2 Curve A I l I I I I 3J RF Tank Current DC. Plate Current k INVENTORS George Rolston 0nd -Zrnest G.Goggio.

ATTORNEY WITNESSES: ay/44, MA

p 1952 I G. RALSTON ET AL 2,611,020

CRYSTAL OSCILLATOR ULTRAMICROMETER Filed March 16, 1949 2 SHEETS-SHEET 2 O U 2 E Fig.4. x C O "-I 0:

Fig.5.

RF. Tank Voltage Distance of Coil from Plale Pl te Current Plate Current Distance of Call from Plale Di stance of Coilfrom Plate INVENTORS WITNESSES g.7. George Ralslon and BYErnest C. Go'ggio.

ATTORNEY Patented Sept. 16, 1952 TJE'D PATENT orrlce -QISTALOSCILLAIOR ULrRaMroaoMrrrEn "George 'Ralston, Wilkinsburg, la., and Ernest Charles Gogg im BaItimore; Mel, assignors to Westinghouse Eiectric CorporationQEast Bittse .:burgh,i:Pa.,:a cerporation :of Pennsylvania Apr'ilicafiorilllafih 16, 1949,1SerialNo; 81:; 656

-1 i'rhi's invention relates to "a crystal oscillator ultra-micrometer'fand, more, particularly, to'a me n a a us" f r -m asu s a l d s- "tance' variations.

rer'fe n ihe, in n im' d an ee ,ie :5

""cf the high sensitivityiand great 'sta bilityof an electron tube oscillator usinga crystalffor ire- 'quency control and whereinthe plate tank coil has" its inductance controlled by thejpresen'ce. of "a metaljplate, which .may "be imovable, thereby producing variations infthe energy generated by the oscillator.

Particular interest is centered inmeasuring ar- ":rangementsof "the typein 'whic'hlthe obj e'ctwhoseo, relative location is to be. measuredfi's not con- "tacted, as "maynccur in .a variety fof laboratory 1 measurements; in fact, "such contact in many cases would not .befpermissible; as when the object is .in'motionaswill be thefc'ase in many in- L'dustrialmeasurem'ents.

' While non 'contactingmeasuring devioes ofier "the rather .wide opportunity of measuring 'changesin capacitanca'inductance or resistance, the attempts made in thegpast'alo'n'g this line have not beensatisfactory,particularly in the range of very small distance variations. In

* measuring thecapacltance between'the plate and an fobject; it is a disadvantage ithatthelnounting of the plate is' necessarily rigid and must be '10- oscillator used in; producing the beat are extreme "ly rigid. In case where! it isa question of measuring the mutual inductance ibe'tween two coils,

ance method impracticablewhen 'thelSiZB-OI the coil is limited. 'Again, in. case of the resistance method utilizing a" plate offering R.-F.' resistance and brought near the coil of the oscillator tank oated in'proximitytothe object, and'that the I fstabilityrequirements of the constant irequency "lrnown apparatus is such'as to'makethe lnductcircuit, appreciable sensitivity can be realized 40 only if the plate be of'highiresistancematerial. In'fact, all of these pricr'art instancescan measure'at best onlyabout a 100 microamperechange per imil /1on0") heightordistance, variation.

' "-It ispaccordin'gly,'an'object'of thisinvfentionto provide a highly sensitive electronici'ultrasmi- It ls'alsoan object ofthisinvention toprovide fan electronic ultra-micrometer whi'chiis .no't'only very "sensitive but one which will "measure- 'extremely small distances, and at .the sametime,

*one wherein the pick-up head istsimple' and noncritical respecting its distance to theln'etaliplate.

'It is" another object of the inventionto. provide an electronic ultr'a micro'me'ter which is not relf Claiins. 615177- 351) stricted as to therange of resistivityci the metal plate.

'It is a further object of the invention taprovide a measuring device wherein the produced energy variations are substantially linear with distance.

' According'to the invention there is'provided 'a highly sensitive, preferably crystal controlled, electron tube oscillator having a plate-tank circuit. By tuning the tank circuit atnear resonance, a range of D.-C. plate current 0r'A.--C. tank current, values substantially linear with capacitor setting is obtained. *With the tank circuit thus tuned, the inductance variations in-the coil thereof, due to distance changes therefrom of a metal plate, are utilized to produce corresponding current changes in the oscillator nlate circuit or voltage changes in the tank circuit. A resistance load circuit which may be adjustable is coupled in the plate circuit and means is in- 'cluded for feeding a predetermined amount of the voltage drop thereacross to an indicator such as an oscilloscope. This feeding means may include one or more amplification stages.

The foregoin and other objects of the invention'and the invention itself will be better understood from the following detailed description of an embodiment thereof taken in connection'with the accompanying drawings in which:

Figures la and lb are diagrammatic view of '"plate'and tank current characteristics of an os- .Figure .5" is a simil'ar :graph "but showe ing. dilferent sensitivitiesias based on .diflerent' parametric values.

Figure 6' isa graph showing a platecurrent- .coiljdistance characteristic ofltheioscillator.

Figure 7'is a graph similar to" that of Fi'g'ure' 6 showing different sensitivities based onthe, plate current-coil distance characteristic as deterpoint 4.

3 mined by different parametric values of the coil distance.

Referring to Figure 1a, there is here indicated the changes in D.-C. plate current and A.-C.

tank circuit current as an oscillator of the type shown in Figure 1b is tuned by its tank capacitor through various angles of its setting. Capacitor plate setting is plotted as the abscissa and R. F. tank current and D. C. plate current as ordinates. Curve A represents P... F. tank current and curve B represents D. C. plate current. It will be noted that the oscillator circuit as shown in Figure 1b, and which in itselfis known, has a frequency controlling crystal 8 connected across a grid resistance 51 in the grid cathode circuit of the oscillator tube 1, and a tunable plate circuit, comprising a tank capacitor and a tank inductance 9. An ammeter 3| is connected in the tunable plate circuit to read R. F. tank current. An ammeter 33 is connected in series with D. C. plate supply terminals 35 to read D. C. plate current. With suitable energizing voltage values assigned to the oscillator, then as the tank capacitor i is tuned from a zero position wherethe D.-C. plate current has a given value at I (curve B), this value remains practically constant until'a point 2 is reached corresponding in a particular case to, say, 87 degrees of the capacitor setting where this plate current suddenly drops to a given value at 3. Thereafter, as the capacitor i0 is further adjusted in the same direction, the value of this plate current drops further and substantially linearly to a Still further tuning of the capacitor l0 will cause the D.-C. plate current to rise substantially to its first value as indicated at and I thereafter practically continue constant. Meanwhile, at a'tuning point indicated at 3, corresponding to 3, the A.-C. tank current begins to critical range of capacitor setting in which current-flow is substantially linear with said setting. In Figure 2 there is illustrated a circuit of an oscillator of the above mentioned type, with indicated connections therefrom adapted to produce the curves shown in Figures 4-7. For the metal plate a copper plate M was used whose distance from the tank coil could be varied by a micrometer screw device l3 to which the copper plate [4 was attached, the mechanical set-up of which is shown in Figure 2a. This. oscillator comprises an electron tube 1 which, though shown as a triode, may be any suitable type of a tube, having in its grid cathode circuit a control crystal 8, and in its plate-cathode circuit, a tank circuit comprising an inductance coil 9 and variable capacitor [0, one terminal of the tank circuit being connected through a blocking condenser 31 to the plate electrode 39 of the tube 1 and the other terminal to the cathode M. The plate 39 of the oscillator tube 1 is shunt-fed through an inductance II which is coupled at its lower terminal by a blocking condenser 43 tothe said cathode. Radio frequency voltage is obtainable by coupling to the tank coil 9. D. C. plate potential is supplied to terminals 35 which are connected in series with a D. C. plate current ammeter 33, across the blocking condenser 43. The cathode 4| of the oscillator tube is grounded at 41. By adjustment of the micrometer screw device l3, the distance between the copper plate 14 and the tank circuit coil 9 may be varied to vary the inductance of the oscillator tank circuit and thus produce the aforesaid changes in R. F. tank voltage or D.-C. plate current.

The arrangement shown in Figure 3 represents the essentials of a complete circuit diagram of one embodiment of the invention, and employs the same reference characters for corresponding parts of Figure 2. Additionally, there are details of the D.-C. plate current output circuit, comprising a measuring series resistance [5 and a balancing circuit including a final recording resistance It having one of its terminals connected to the cathode end of resistance I5 and its other terminal connected by way of a potentiometric resistance l1 and slider 18 to-the other terminal of resistance l5, said potentiometric resistance being energized by any suitable source l9. Said other end of resistance I6 is coupled by lead 49 to an indicating system.

When it is deemed advisable to increase the D.,-C. output of the oscillator or to improve the correlation between oscillator and indicator, a direct current amplifier may be used. As shown, this amplifier comprises a pentode tube 20, which could be any other suitable tube, to whose control grid 53 the said lead 49 is connected. The

cathode 55 of this pentode is grounded at,,5l through a biasing parallel resistance condenser combination 2i and the output is derived from an adjustable contact on a series resistance 22 in the plate circuit with ground return or equivalent,.such output being extended by a lead 25 to an oscilloscope 23. Since the oscilloscope it self and its mode of operation are well known it is not necessary to show or describe it in detail.

The object 59 in which height variations are to be determined, is placed in the field of the tank inductance coil 9.

In operation, it is obvious that, with proper adjustment of the above described circuit apparatus, the beam of the oscilloscope will be deflected a given amount in dependence on'the value of current derived from the oscillator through the amplifier, when used, such current value in turn varying with the proximity to the tank coil 9 of the object 59, height variations of which are to be determined. The screen of the oscilloscope may be calibrated so that such distances can be directly read thereon. For the purpose of calibration the micrometer screw device |3 shown in Figure 2a may be used. By adjustment of the micrometer screw, the copper plate [4 may be made to change its position with respect to the coil 9 by a known amount, and the oscilloscope beam is deflected accordingly. Thus a certain oscilloscope deflection corresponds to an accurately measured height or distance variation. This calibration is independent of tube condition and exact value of plate or filament voltage.

Referring now to Figures 4 and 5, there are here shown sensitivity curves based on the tank voltage versus distance of coil 9 from plate i4 characteristic of the crystal oscillator operated in the manner above described. From this characteristic as shown in Figure 4 a sensitivity of the order of 53 millivolts per mil was obtained. In Figure 5 are shown a plurality 'ofsuch curves based on different parametric values efiected by adjustment of plate current of the oscillator, the respective curves showing increasing values of sensitivity as 87, 122 and 147 millivolts per mil.

In Figs. 6 and 7 the curves are analogous to those above described but are based on the plate current-distance of coil 9 from plate [4 characteristic which exhibits a high sensitivity for small height variations. From these curves, a sensitivity as high as 2 ma. per mil is shown, and from this characteristic a high sensitivity of 3 ma. per mil has been obtained with no loss in stability. The curves of Figure '7 indicate a range of sensitivity varying with the parametric ranges of distance of coil from plate.

The crystal oscillator ultra-micrometer as hereing described is not only a highly sensitive instrument for measuring small distances but also one which can be made to measure extremely small distance or height changes, the only practical limit in this respect being the stability of the oscillator. With a galvanometer requiring .0047 ma./mm., this device will measure down to 4.25 10- inches, when using a sensitivity of 2 ma. per mil.

It is obvious that considerable latitude exists respecting the design of a circuit apparatus according to the invention. By way of example only, one set of values of circuit elements which has been found suitable is as follows, referring to Figure 2: Crystal 8, 3.807 megacycles, grid leak resistance 51, 10 megohms, tank coil 9, 2 microhenries, tank capacitor l0, 500-4000 micromicrofarads, R. F. choke l I, 50 millihenries, blocking condensers 31, 43, .01 microfarad.

Other obvious variations within the scope of the invention are possible and the invention is not to be regarded as limited by the use of specific elements employed in describing it unless expressly so indicated.

We claim as our invention:

1. An electronic ultra micrometer for measuring distance variation between two elements comprising a crystal controlled electron tube oscillator comprising an oscillator tube having a cathode, a plate, and a grid and having a tank circuit including an inductance and a capacitance, means for tuning said tank circuit, said inductance constituting the first of said elements, the second of said elements being of metal and positioned in the field of said inductance and means for measuring variations of energy in the tank circuit of said oscillator corresponding to variations in distance between said elements, said tank circuit being adjusted so that the region of operation of the circuit is on the steep portion of the oscillator plate current characteristic, in which region a tank circuit inductance effect corresponding to a relatively small variation in distance between said elements will produce a relatively large change in the oscillator plate current.

2. An electronic ultra micrometer according to claim 1, wherein said energy variation characteristic is that of oscillator plate direct curren 3. An electronic ultra micrometer according to claim 1, wherein said energy variation characteristic is that of the tank circuit oscillation.

4. An electronic ultra-micrometer according to claim 1, wherein said energy variation is that of the direct current in the oscillator plate circuit and there is included an oscilloscope indicating system and means for coupling said indicating system to said plate circuit, including a balancing circuit comprising a resistance in said plate circuit and an output resistance in series with a potentiometric resistance connected in parallel with said plate resistance.

GEORGE RALSTON. ERNEST CHARLES GOGGIO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,778,827 Evans Oct. 21, 1930 1,848,490 Nicolson Mar. 8, 1932 1,946,924 Allen Feb. 13, 1934 2,083,759 Temple June 15, 1937 2,261,815 Thompson Nov. 4, 1941 2,414,224 Douglas Jan. 14, 1947 2,439,047 Grinstead Apr. 6, 1948 2,452,156 Schover Oct. 26, 1948 FOREIGN PATENTS Number Country Date 275,741 Great Britain Feb. 17, 1927 

